Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 18-31; DOI: 10.3221/IGF-ESIS.40.02 23 h [mm] D [mm] Number of tests Number of specimens with strain gages Uniaxial compressive strength [MPa] Intact rock modulus E [MPa] Poisson’s ratio v Average [MPa] St. Dev. [MPa] Average [MPa] St. Dev. [MPa] Average St. Dev. 110 54 6 6 35.56 0.51 13575 193 0.221 0.007 150 75 6 6 33.81 0.73 13318 733 0.238 0.022 200 100 6 6 32.09 1.82 13735 1272 0.242 0.015 Table 2: The experimental results of the uniaxial compression tests for Alfas stone. (a) (b) (c) (d) Figure 5: Typical diagrams for uniaxial compression tests. (a) Stress-strain curves from the three biaxial strain-gages, (b) Mean value stress-strain curves, (c) Intact rock modulus and (d) Poisson’s ratio in correlation with the uniaxial stress. Three different failure modes were observed during the uniaxial compression tests of Alfas stone. Some specimens failed along single shear planes (Fig. 6a), others failed in axial splitting (Fig. 6b) and a third group failed along conjugate shear planes (Fig. 6c). It should be noted that in all cases specimens exhibit extensive spalling before failure. Size effect for uniaxial compression tests Α total of 18 uniaxial compression tests were completed in order to investigate the size effect for the Alfas natural building stone under uniaxial compression. Initially, the mean curves of intact rock modulus and Poisson’s ratio, for each set of cylindrical specimens, are plotted in correlation with the uniaxial stress (Fig. 7). For the case of Poisson’s ratio (Fig.7b) the trend of these curves is similar for all diameters, while for the intact rock modulus (Fig.7a) this similarity is only observed for stresses greater than 50% of specimen strength.